Effects of ZrO2 nanoparticles on the mechanical properties of Sn-Zn solder joints on Au/Ni/Cu pads

The shear strength of Sn-9Zn and Sn-9Zn-ZrO2 Solder balls on electrodeposited Ni/Au BGA joints after multiple reflows was investigated by shear tests and microstructural observations. ZrO2 nanoparticles in the solder balls improved the shear strength and the reliability of solder joints after multiple reflows significantly. They embedded in the solder matrix to obstruct the motion of dislocations by pinning and also pinned grain boundaries so as to improve the shear strength of the solder matrix. At the same time, due to the strong adsorption effect of Zn atoms, the ZrO2 nanoparticles absorbed Zn atoms on their surfaces so as to impede them from gathering on the surfaces of the Ni-Zn IMC layers to give excessive growth, and, as a result, this improved the reliability of solder joints significantly. (C) 2008 Elsevier B.V. All rights reserved.